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A province-wide evaluation of the amount, distribution, source and control of damage to Ontario apple trees was initiated. Data we re obtained from 280 responses to a questionnaire distributed to growers across Ontario, and from trap censuses in three widely separated areas. Meadow voles (Microtus pennsylvanicus) damaged or destroyed 8,423 trees in our questionnaire sample and other mammals damaged another 10,307 trees. No relationship was found between application of rodenticide and levels of damage, but rodenticide-treated baits sharply reduced numbers of voles on our trap plots. Orchards with high levels of damage were on average only one-third as large as the average orchard in our total sample. All damage by voles appeared to be caused by meadow voles and no pine voles (M. pinetorum) were found. Numbers of voles varied greatly among our three study areas. Future work will concentrate on factors causing high levels of damage and on the relationship between dispersal of voles and the effects of rodenticide treatment.